JP2007504663A - Thermally conductive materials using conductive nanoparticles - Google Patents

Abstract

Thermal interface compositions contain both non-electrically conductive micron-sized fillers and electrically conductive nanoparticles blended with a polymer matrix. Such compositions increase the bulk thermal conductivity of the polymer composites as well as decrease thermal interfacial resistances that exist between thermal interface materials and the corresponding mating surfaces. Such compositions are electrically non-conductive. Formulations containing nanoparticles also show less phase separation of micron-sized particles than formulations without nanoparticles.

Description

  The present disclosure relates to the use of conductive nanoparticles in combination with micron sized non-conductive fillers to improve the thermal conductivity of a polymer matrix.

  Many electrical components generate heat during operation. If such heat is not efficiently removed from the electrical components, heat will accumulate. As a result, malfunction or permanent damage of electrical components can occur. For this reason, thermal management techniques are often used in electrical circuits and systems to facilitate heat removal during operation.

  Thermal management techniques often use a form of heat sink to dissipate heat from the high temperature region of the electrical system. A heat sink is a structure made of a material with high thermal conductivity (eg, typically a metal) that is mechanically coupled to an electrical component to aid in heat removal. In a relatively simple form, the heat sink is made of a piece of metal (eg, aluminum or copper) in contact with the electrical circuit in operation. Heat from the electrical circuit flows into the heat sink through the mechanical contact surface between the units.

  In a typical electrical component, the heat sink is heated by placing the heat sink plane against the electrical component plane during operation and holding the heat sink in place with some form of adhesive or securing means. Mechanically coupled to the part. As will be appreciated, there are usually voids between the surfaces of the heat sink and the surface of the component, since they are rarely perfectly flat or smooth. As is well known, the presence of voids between two opposing surfaces reduces the ability to transfer heat through the contact surface between the surfaces. Such voids reduce the effectiveness and value of the heat sink as a thermal management device. In order to address this problem, polymer compositions called thermal interface materials (TIMs) have been developed that are placed between heat transfer surfaces to reduce the thermal resistance between them. Many TIM applications, including those used for electrical components, require that the TIM be electrically insulating. Also, in many TIM applications, if the coefficient of thermal expansion (CTE) of the heat-generating component is significantly different (high or low) from the CTE of the heat sink, the TIM must be sufficiently capable of mechanical isolation between the heat-generating component and the heat sink. Don't be. The TIM thickness and material composition may be limited by mechanical compliance requirements. The minimum thickness of the TIM depends on the degree of planarity of the surfaces of both the heat generating component and the heat sink.

  The overall thermal conductivity of current thermal conductive material is greatly limited by the low thermal conductivity of the polymer matrix (about 0.2 W / m-K for the polymer normally in TIM). In order to increase the thermal conductivity of these TIMs, many TIM materials are filled with particles with higher thermal conductivity (> 10 W / m-K). According to one estimate ("Thermal Conductive Polymer Compositions," DM Bigg., Polymer Compositions, June 1986, Vol. 7, No. 3), the overall maximum heat achievable with electrically insulating polymer composites. The conductivity is only 20-30 times that of the base polymer matrix. This number hardly changes regardless of the type of filler when the thermal conductivity of the filler exceeds 100 times the thermal conductivity of the base polymer matrix. Accordingly, the thermal conductivity of the polymer material is lower than that of the heat sink, and as a result, heat transfer from the heat-generating component to the heat sink is insufficient. In addition, 1) micro- or nano-voids, and 2) in the layer lacking filler due to the sedimentation of the filler or the irregularity of the surface smaller than the particle size of the filler cannot enter the micron-size filler. Due to the resulting interface defects, the effective heat transfer performance is further reduced.

  While metals and other conductive materials are often thermally conductive materials, in non-conductive applications these high performance materials cannot be used for TIMs or must be coated with non-conductive materials. This increases the cost, reduces the thermal performance and risks the possibility of gaps in the non-conductive coating that can potentially cause electrical shorts. Thus, in most cases, non-conductive materials must be used, which limits material selection and generally limits thermal conductivity.

  Attempts to increase the thermal conductivity of TIMs include the use of nanoparticles in addition to fillers. For example, US patent application Ser. No. 10 / 426,485 discloses the use of non-conductive nanoparticles in a polymer matrix to improve the thermal conductivity of TIM systems. However, for the reasons noted above, the choice of materials for use as nanoparticles is limited.

Other thermal cooling means are utilized for other electrical components that generate relatively low heat during operation. These parts are often used in portable electronic devices such as laptop personal computers, mobile phones, personal digital assistants and digital cameras. These parts are often mounted on printed wiring boards made of polymer material by an array of solder balls. Due to environmental concerns and reliability concerns regarding the integrity of solder joints during normal thermal cycling based on power cycling, resin underfill materials are used to fill the gaps between the solder balls under the electrical components. ing. In many applications, the primary thermal cooling path is from the component to the printed wiring board. Even if there is no underfill or there is an underfill that does not conduct heat well, the only way for the heat from the component to the wiring board is solder. This thermal performance can be improved by adding a thermally conductive filler to the underfill resin. In this field of application, the resin must not be conductive because the component I / O pads must be shorted. Therefore, underfill resins are limited to the use of non-conductive fillers. As with TIM materials, this is a limit on the thermal conductivity that can be reached. Therefore, there is a need for improved compositions that efficiently transfer heat between a printed wiring board and a heat generating component with a non-conductive underfill material.
US patent application Ser. No. 10 / 426,485 US Pat. No. 6,500,951 US Pat. No. 6,265,471 US Pat. No. 6,060,539 US Pat. No. 5,695,872 US Pat. No. 5,026,748 "Thermal Conductive Polymer Compositions," D. M.M. Bigg. , Polymer Compositions, June 1986, Vol. 7, no. 3 “Polymer Handbook”: Branduf, J .; Immergut, E .; H; Gulke, Eric A; Wiley Interscience Publication, New York, 4th ed. (1999) “Polymer Data Handbook” Mark, James Oxford University Press, New York (1999) “Chemistry and Technology of Silicone”, Noll, W .; Academic Press 1968 “Chemistry and Technology of the Epoxy Resins”. Ellis (Ed.) Chapman Hall, New York, 1993 "Epoxy Resins Chemistry and Technology", edited by C.I. A. May, Marcel Dekker, New York, 2nd edition, 1988

  Therefore, there is a need for improved compositions that efficiently transfer heat between a heat sink and a heat generating component, particularly in non-conductive applications.

  The thermally conductive composition of the present disclosure is a polymer matrix that includes both non-conductive micron-sized filler particles and conductive nanoparticles. The thermally conductive material of the present disclosure is non-conductive. The thermally conductive composition of the present disclosure can be used as a thermally conductive material between a heat sink and an electrical component or as an underfill material for an electronic component in a portable electronic device.

  The disclosure also describes a heat generating component and an electronic component including a heat sink or heat sink, each in contact with a thermally conductive composition that includes both non-conductive micron-sized filler particles and conductive nanoparticles. . In one embodiment, the electrical component is a chip that includes a printed wiring board.

  The heat transfer efficiency improving method of the present disclosure includes a step of interposing a heat conductive composition including both non-conductive micron-sized filler particles and conductive nanoparticles between a heat-generating component and a heat sink or heat sink. . Where the heat generating component is a chip, the heat conducting composition is placed between the chip and the printed wiring board.

  In another embodiment, the heat transfer efficiency improving method of the present disclosure includes a step of interposing a heat conductive composition including conductive nanoparticles between a chip and a printed wiring board in an application where large particles cannot be used. included.

  The present disclosure provides a thermally conductive composition comprising both non-conductive micron-sized filler particles and conductive nanoparticles in a polymer matrix. Conductive nanoparticles are used to increase the thermal conductivity of the thermally conductive composition. As used in this disclosure, a “thermal conductive composition” is any material that helps remove heat from a high temperature region in an electrical device, and is a thermal conductive material placed between a heat sink and a heat generating component of an electrical device. Integrated circuit package to improve the fatigue life of the solder used in the chip by filling material ("TIM") or the gap between the chip and the substrate and removing the heat generated during the thermal cycle In other words, the underfill material used in the chip can be included. The present disclosure includes non-conductive micron-sized fillers, including conductive nanoparticles, that are particularly suitable for use in applications where micron-sized particles cannot be used due to mechanical or optical requirements. There is also provided a non-heat conducting composition. These applications include non-flowable underfill applications where micron-sized or larger particles are known to cause solder joint defects, wafer level under-requirements where a transparent resin is required for wafer cutting. Including, but not limited to, fill applications and underfill applications in the installation of optical communication devices where micron-sized particles cannot be used due to the optical properties of the resulting material.

  The thermally conductive composition itself is non-conductive. A matrix comprising non-conductive micron-sized filler particles and conductive nanoparticles of the present disclosure can reach higher thermal conductivity than a comparative blend of non-conductive micron-sized filler particles and matrix alone . The nanoparticles thus increase the overall thermal conductivity of the matrix, while at the same time maintaining a viscosity that is not lost in ease of processing and manipulation. In addition, the nanoparticles can penetrate into surface micropores and irregularities that are not reachable by micron-sized fillers, thereby reducing the effect of surface resistance.

The organic matrix utilized in the present disclosure can be any polymeric material, including curable and non-curable matrices. Suitable organic matrices include polydimethylsiloxane resin, epoxy resin, acrylic resin, other organofunctional polysiloxane resin, polyimide resin, fluorocarbon resin, benzocyclobutene resin, fluorinated polyallyl ether, polyamide resin, polyimide amide resin Phenol resole resin, aromatic polyester resin, polyphenylene ether (PPE) resin, bismaleimide triazine resin, fluororesin and any other polymer system known to those skilled in the art, but is not limited thereto. (For general polymers, "Polymer Handbook" :, Branduf, J,;. Immergut, E.H; Grulke, Eric A;. Wiley Interscience Publication, New York, 4 th ed (1999) and "Polymer Data Handbook "See Mark, James Oxford University Press, New York (1999)).

  Preferred curable polymer matrices include free radical polymerization, atom transfer radical polymerization, ring-opening polymerization, ring-opening metathesis polymerization, anionic polymerization, cationic polymerization and other acrylic resins and epoxy resins that can form a crosslinked network by methods known to those skilled in the art Polydimethylsiloxane resins and other organofunctional polysiloxane resins. Suitable curable silicone resins include, for example, “Chemistry and Technology of Silicone”, Noll, W .; An addition curable and condensation curable matrix as described in Academic Press 1968.

  If the polymer matrix is not a curable polymer, the resulting heat transfer composition can be a gel, grease or phase change material that can keep the parts from separating during heat transfer during molding and operation of the device. It is possible to build.

  The second component of the composition of the present disclosure is a number of one or more micron sized fillers. Micron-sized fillers are thermally conductive materials and may be reinforcing or non-reinforcing. Suitable micron-sized fillers include fumed silica, fused silica, finely divided quartz powder, amorphous silica, carbon black, graphite, diamond, hydrated alumina, metal nitrides (eg, boron nitride, aluminum nitride, And silica coated with aluminum nitride), metal oxides (eg, oxides of aluminum, magnesium, zinc, titanium, zirconium, beryllium, or iron) and combinations thereof. The filler is typically present from about 10 to about 95% by weight, based on the weight of the total final composition. More generally, the filler is present from about 30 to about 90% by weight, based on the weight of the total final dispersion composition.

  The particle size of the micron sized filler particles is in the range of about 1 to about 100 microns, with a range of about 10 to about 50 microns being preferred. The choice of micron-sized filler size is determined by the target adhesive layer thickness in its end use, usually from about 10 to about 150 microns. The size of the filler particles should be less than the cured thickness of the heat conductive composition in which it is used.

  The third component of the composition of the present disclosure is conductive nanoparticles. The conductive nanoparticles used in the present disclosure are made of a metal such as copper, silver, gold, platinum, palladium, graphite or aluminum, or a semiconductor material such as doped silicon or silicon carbide. The conductive nanoparticles used in the present disclosure do not require a non-conductive coating on their surface.

  When used in thermally conductive compositions with micron sized fillers, the conductive nanoparticles are usually in the range between about 3% and about 50% by weight, preferably based on the weight of the total final composition. Is included in the range of about 10% to 30% by weight. This range corresponds to a range of about 1% to about 25% of the thermally conductive composition by volume, preferably about 2% to about 15% of the total final composition by volume.

  When used in thermally conductive composition applications where micron sized particles cannot be used due to mechanical or optical requirements, the conductive nanoparticles are typically about 10 to about 85 weight based on the weight of the total final composition. %, Preferably about 50 to about 75% by weight.

  Preferably, the conductive nanoparticles are of a size in the range of about 1 to about 250 nanometers, with a range of about 10 to about 100 nanometers being preferred.

  Although the thermally conductive compositions of the present disclosure are well suited for use in non-conductive applications such as TIMs, the compositions of the present disclosure are also required to be non-conductive, but the thermal conductivity Resin systems for non-TIM applications that require other material property improvements such as modulus, dielectric constant or refractive index can also be used. Such materials include molds, overmolds, underfills, wafer level underfills, non-flowable underfills and interposers.

  Although the addition of micron sized fillers substantially increases the thermal conductivity of the composition, the effect of micron sized fillers on the thermal conductivity of the polymer matrix is greatly amplified by the addition of conductive nanoparticles. Conductive nanoparticles in a region where one micron sized particle touches or is very close to another micron sized particle thermally connects one micron sized particle to another. This creates a heat path between the micron-sized particles in parallel with the direct heat conduction path between the micron-sized particles. In this way, the thermal coupling from particle to particle and from particle to surface is enhanced.

  As an example, if a polymer matrix such as epoxy aramid having a thermal conductivity of about 0.12 W / m-K is added with 80-90 wt% of a suitable micron-sized filler, the thermal conductivity of the polymer matrix is about 2. It can be increased to 0 W / m-K. However, by adding 20-40% by weight of the conductive nanoparticles of the present disclosure, the initial thermal conductivity of the polymer matrix can be increased to 0.4-0.6 W / m-K and does not contain nanoparticles. It can be 3 to 5 times compared to the composition. Thus, for example, if the thermally conductive composition is TIM, adding 70-80% by weight of a suitable micron-sized filler to the resin containing nanoparticles results in the inclusion of nanoparticles. A TIM of 4.0 to 6.0 W / m-K, which is 2 to 3 times higher than a non-TIM If only micron particles are added until the same high thermal conductivity is reached, the resulting composition becomes very viscous and difficult to process, to produce electronic devices, especially semiconductor chips such as flip chip devices. The necessary fluidity is lost. Furthermore, if the conductive nanoparticles are filled at a high weight percentage that falls in the range of 80-90%, the TIM will become conductive. On the other hand, using the conductive nanoparticles of the present disclosure increased the viscosity of the filled resin, which can be used commercially while maintaining electrical insulation, without greatly increasing the flow properties until insufficient. Thermal conductivity can be obtained.

  In the compositions of the present disclosure, micron particles are about 100-5000 times larger than nanoparticles. Accordingly, the TIMs of the present disclosure have an adhesive layer with a thickness in the range of about 10 to about 150 microns, more preferably in the range of about 20 to about 70 microns.

  According to the present disclosure, conductive nanoparticles typically have a higher thermal conductivity than non-conductive nanoparticles (coated or uncoated) and are less expensive to manufacture than coated nanoparticles. Phase separation between filler and resin is unlikely to occur, shelf life is increased, and product stability is also obtained.

  Micron-sized fillers and conductive nanoparticles are blended with an organic matrix to form the composition of the present disclosure. One or more solvents can be added to the composition as appropriate to facilitate blending the nanoparticles and micron sized fillers with the organic matrix. Suitable solvents include, but are not limited to, isopropanol, 1-methoxy-2-propanol, 1-methoxy-2-propyl acetate, toluene, xylene, n-methylpyrrolidone, dichlorobenzene, and combinations thereof.

  The method of blending nanoparticles and micron-sized fillers with the organic matrix is not critical.

  The composition can be treated with an acid or base or with an ion exchange resin to remove acidic or basic impurities. The composition is evacuated at a temperature between about 0.5 Torr (0.066 kPa) and about 250 Torr (3.3 kPa) and between about 20 ° C. and about 140 ° C. to remove solvent, residual water Advantageously, any low boiling components such as, and combinations thereof can be substantially removed. The result is a nanoparticle and micron sized filler dispersed in an organic matrix, referred to in this disclosure as the final dispersion or final composition. Substantial removal of low boiling components is defined in this disclosure as removal of at least about 90% of the total amount of low boiling components.

  The presence of nanoparticles in the composition of the present disclosure also improves the stability of the composition when micron sized fillers are included. The nanoparticles prevent or reduce the settling of micron sized fillers, thereby reducing the likelihood of a filler-free layer in the interface material. Thus, the conductive nanoparticles of the heat conductive composition of the present disclosure can also be used to retard phase separation of polymer compositions containing micron sized fillers. The polymer composition is prepared by providing a polymer matrix, blending it with a micron particle size filler to make the polymer composition, and then blending the conductive nanoparticles with the polymer composition.

  The compositions of the present disclosure may also include other added materials. For example, a curing catalyst can be added to the final dispersion to promote curing of the final composition. Usually the amount of catalyst added ranges between about 10 parts per million (ppm) and less than about 2% based on the weight of the entire composition to be cured. Examples of cationic curing catalysts include bisallyliodonium salts (eg, bis (dodecylphenyl) hexafluoroantimonate, iodonium hexafluoroantimonate (octyloxyphenyl, phenyl) iodonium, bisallyliodonium tetrakis (pentafluorophenyl) borate). ), Triallylsulfonium salts, and combinations thereof, including but not limited to. Radical curing catalysts include various peroxides (eg tert-butylperoxybenzoate), azo compounds (eg 2,2′-azobis-isobutylnitrile) and nitroxides (eg 4-hydroxy-2,2,6,6-). Tetramethylpiperidinyloxy (ie, 4-hydroxy TEMPO)), but is not limited thereto. Preferred catalysts for addition curable silicone resins are various Group 8-10 transition metal (eg ruthenium, rhodium, platinum) complexes. Preferred catalysts for condensation curable silicones are organotin or organotitanium complexes. The detailed structure of the catalyst is known to those skilled in the art.

  For the cationic curable polymer matrix, an effective amount of a free radical generating compound can be appropriately added as a reagent for use. Suitable free radical generating compounds include aromatic pinacols, benzoin alkyl ethers, organic peroxides, and combinations thereof. Free radical generating compounds promote the decomposition of onium salts at relatively low temperatures.

  To the epoxy resin, a curing agent such as a carboxylic anhydride curing agent and an organic compound having a hydroxy group can be added as a reagent for use together with a curing catalyst. In these cases, the curing catalyst can be selected from, but not limited to, amines, alkyl-substituted imidazoles, imidazolium salts, phosphines, metal salts, triphenylphosphine, alkyl-imidazoles, aluminum acetylacetonates, and combinations thereof. Not. A curing agent such as a polyfunctional amine can be used in combination as a crosslinking agent. Exemplary amines include ethylene diamine, propylene diamine, 1,2-phenylene diamine, 1,3-phenylene diamine, 1,4-phenylene diamine, and any other compound containing two or more amino groups. However, it is not limited to these.

  For epoxy resins, typical anhydride curing agents typically include methylhexahydrophthalic anhydride, 1,2-cyclohexanedicarboxylic anhydride, bicyclo [2.2.1] hept-5-ene- 2,3-dicarboxylic acid anhydride, methylbicyclo [2.2.1] hept-5-ene-2,3-dicarboxylic acid anhydride, phthalic acid anhydride, pyromellitic dianhydride, hexahydrophthalic acid anhydride Products, dodecenyl succinic anhydride, dichloromaleic anhydride, chlorendic anhydride, tetrachlorophthalic anhydride and the like. Combinations comprising at least two anhydride hardeners may also be used. Illustrative examples are "Chemistry and Technology of the Epoxy Resins" B. Ellis (Ed.) Chapman Hall, New York, 1993 and "EpoxyResins Chemistry and Technology", edited by CA May, Marcel Dekker, New York, 2nd edition , 1988.

  For addition curable silicone resins, a cross-linking agent such as a polyfunctional Si-H containing liquid silicone may be added at a molar ratio of Si-H to vinyl of 0.5 to 5.0 and preferably 0.9. It can be used in combination so as to fall within the range of ~ 2.0.

  For addition curable silicone resins, inhibitors can be included as appropriate to improve the curing properties and achieve the desired shelf life. Inhibitors include, but are not limited to, phosphine compounds, amine compounds, isocyanurates, alkynyl alcohols, maleates and other compounds known to those skilled in the art.

  Reactive organic diluents may also be added to the overall curable composition to reduce the viscosity of the composition. Examples of reactive diluents include 3-ethyl-3-hydroxymethyl-oxetane, dodecyl glycidyl ether, 4-vinyl-1-cyclohexane diepoxide, di (beta- (3,4-epoxycyclohexyl) ethyl) -tetra Includes methyldisiloxane, various dienes (eg 1,5-hexadiene), alkenes (eg n-octene), styrenic compounds, compounds containing acrylates or methacrylates (eg methacryloxypropyltrimethoxysilane) and combinations thereof However, it is not limited to these. Non-reactive diluents may also be added to the composition to reduce the viscosity of the formulation. Examples of non-reactive diluents include low boiling aliphatic hydrocarbons (eg, octane), toluene, ethyl acetate, butyl acetate, 1-methoxypropyl acetate, ethylene glycol dimethyl ether, and combinations thereof. It is not limited.

  Adhesion promoters can also be added to the final dispersion, including trialkoxyorganosilanes such as γ-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, bis (trimethoxysilylpropyl fumarate). )) Is included and is used in an effective amount, usually in the range between about 0.01% and about 2% by weight of the total final dispersion.

  The flame retardant can be added to the final dispersion as appropriate, in the range between about 0.5% and about 20% by weight relative to the total final composition amount. Examples of flame retardants include phosphoramide, triphenyl phosphate (TPP), resorcinol diphosphate (RDP), bisphenol-a-diphosphate (BPA-DP), organic phosphine oxide, halogenated epoxy resins (tetra Bromobisphenol A), metal oxides, metal hydroxides, and combinations thereof are included.

  Other non-conductive nanoparticles that have a higher thermal conductivity than the organic matrix can also be used in conjunction with the conductive nanoparticles to prepare the compositions of the present disclosure. Additional suitable non-conductive nanoparticles include colloidal silica, polyhedral oligomeric silsesquioxane (“POSS”), nano-sized metal oxides (eg, alumina, titania, zirconia), and nano-sized metal nitrides. (For example, but not limited to boron nitride, aluminum nitride). In a particularly useful embodiment, the additional nanoparticles have functional groups to enhance their integration into the organic matrix, such as organic functionalized POSS materials or colloidal silica. It is. The particle size of colloidal silica is typically in the range between about 1 nanometer (“nm”) and about 250 nm, and more usually in the range between about 5 nm and about 150 nm.

  The final composition can be mixed by hand or by standard mixing equipment such as a dough mixer, change can mixer, planetary mixer, twin screw extruder, two or three roll mill, etc. it can. The blending of the components of the composition can be performed in a batch, continuous, or semi-continuous manner by any method used by those skilled in the art.

  The curing step can be performed by any method known to those skilled in the art. Curing is performed by methods such as thermal curing, ultraviolet curing, microwave curing, electron beam curing, and combinations thereof. Curing typically occurs at a temperature in the range between about 20 ° C and about 250 ° C, more usually in the range between about 20 ° C and about 150 ° C. Curing is typically in the range between about 1 atmosphere (“atm”) (0.10 MPa) and about 5 tons per square inch (77.2 MPa) and more usually about 1 atmosphere (0.10 MPa) and square inches. Occurs under pressures in the range between about 100 pounds per pound ("psi") (0.69 MPa). In addition, curing typically occurs in a time range between about 30 seconds and about 5 hours, and more usually in a range between about 90 seconds and about 60 minutes. The cured composition can optionally be post-cured at a temperature in the range between about 100 ° C. and about 150 ° C. for a time in the range between about 1 hour and about 4 hours.

  The addition of conductive nanoparticles provides an overall base polymer matrix that provides improved thermal conductivity, especially when placed between any two objects in non-conductive applications, such as between electrical component parts. Used to increase the thermal conductivity. Furthermore, the thermally conductive composition of the present disclosure reduces the interfacial resistance to heat flow that is inherently present on the surface of any two parts to which heat is to be transferred. The thermally conductive compositions of the present disclosure can be used in electronic devices such as computers, semiconductors, or any device that requires heat transfer between components.

  In one embodiment, the electronic component includes a semiconductor chip as a heat generating component. In such a case, the heat generating component may be a chip carrier, an area array package, a chip scale package, or other semiconductor package structure. In other embodiments, the semiconductor chip itself is a heat generating component.

  Application of the thermally conductive composition of the present disclosure can be accomplished by any person skilled in the art. Conventional methods include screen printing, stencil printing, injection dispensing and pick and place equipment.

  In another aspect, the composition of the present disclosure can be formed into a sheet and cut into any desired shape. In this embodiment, the composition of the present disclosure can be advantageously used to make a preformed thermally conductive pad that can be placed between electronic components.

  The present disclosure will now be described in further detail with reference to the accompanying drawings. FIG. 1 is a cross section of a non-conductive TIM 10 of the present disclosure. The TIM is placed between the electronic device 12 and a heat sink or heat sink 14. The TIM material is a polymer resin 16 such as an epoxy-based or silicone-based material, which also includes a number of non-conductive micron-sized particles 18 and smaller conductive nanoparticles 20. The TIM typically has an adhesive layer thickness of about 10 to about 150 microns, preferably about 20 to about 70 microns, filling any voids to facilitate heat transfer.

  FIG. 2 is an enlarged cross-sectional view of the TIM system shown in FIG. This figure illustrates two micron sized filler particles 18 and a number of conductive nanoparticles 20. This figure highlights the interfacial area between a micron sized filler particle 18 and the device surface 12 and between two micron sized filler particles. Conductive nanoparticles are present in these interfacial areas as well as within the entire region of resin 16. Significant thermal improvements in this TIM system include three interfacial areas: the area from the micron sized filler particles 18 to the electronic device surface 12, the micron sized filler particles 18 to the micron sized filler particles 18. This is an improved heat conduction effect in the area and surface area (not shown) of the heat sink 14 from the micron-sized filler particles 18.

  FIG. 3 is a cross-section of a TIM enlargement showing conductive nanoparticles 20 and their ability to improve thermal conductivity from micron-sized particles 18 to micron-sized particles 18. Conductive nanoparticles in a region where one micron-sized particle is in contact with or very close to another micron-sized particle thermally couples one micron-sized particle to another micron-sized particle To do. This creates a plurality of heat paths between the micron sized 18 particles in parallel with the direct thermal conduction path between the micron sized particles. As long as the micron-sized particles are non-conductive, the conductive nanoparticles do not create a path for electrical conduction from the device to the substrate.

  However, although it is theoretically possible that the nanoparticles are oriented and the conductive nanoparticles are long and chained to form a direct electrical connection through the TIM adhesive layer, the amount of particles in the TIM Such an orientation is practically impossible due to the combination of and size. Target TIM thickness (within 10 to 150 microns), amount of nanoparticles in TIM (about 3 to about 50% by weight, 1 to 25% by volume), and preferred nanoparticle size (10 to 100 nanometers) In order for the TIM to become conductive, 200 to 5000 conductive nanoparticles that are all in contact with each other in a continuous path are connected in a daisy chain from the surface of the electronic device 12 (heat dissipation). Plate) 14 surface would have to be reachable. As will be readily appreciated by those skilled in the art, electronic devices that will inevitably block short electrical paths created by conductive nanoparticles, especially in the presence of non-conductive particles of micron size, and insulate the overall connection It would be impossible for the conductive nanoparticles to form a continuous current path between the heat sink 12 and the heat sink 14 and thereby form an electrical connection.

  In another embodiment, the composition of the present disclosure can be used in electronic components as an underfill material. In this embodiment, conductive nanoparticles are added to a polymer resin that also contains non-conductive micron-sized particles, but the resulting matrix system is non-conductive and used as an underfill material for electronic components. The The electronic component uses a solder ball to electrically connect the electronic component to a printed wiring board. In such cases, the use of the composition of the present disclosure is usually after assembly of the parts on the printed wiring board and reflow of the solder. Alternatively, an underfill resin can be applied to the wiring board prior to component mounting. In this method, the solder is reflowed while the resin is cured. Another method involves applying a thermally conductive underfill resin to a semiconductor wafer that includes an array of multiple electronic components and solder balls. Following separation into individual parts by wafer cutting, the parts are attached to a printed wiring board. In this method, the solder is reflowed when the resin is cured.

  FIG. 4 shows a heat generating component 30 electrically connected by a solder ball 32 to a printed wiring board 34 with a thermally conductive underfill 36 sealing the component surface 38, the wiring board surface 40 and the solder ball 32. FIG. The thermally conductive resin 16 includes both conductive nanoparticles 20 and non-conductive micron-sized particles 18. The thermally conductive underfill fills the 50-500 micron gap between the component and the wiring board.

  In yet another embodiment, the conductive nanoparticles are added to a polymer resin that does not include micron-sized particles. The resulting matrix system is non-conductive and the resin is used as an underfill material for electronic components that use solder balls to electrically connect the electronic components to the printed wiring board. For these applications, wafers that require a transparent resin for application to non-flowable underfill, where wafers with micron size or larger particles are known to cause defects in solder joints, and wafer cutting Application to level underfill, and application in the installation of optical communication devices where micron-sized particles cannot be used due to the optical properties of the resulting material include, but are not limited to.

  The method of improving heat transfer of the present disclosure includes placing a heat generating component and a non-conductive heat conductive composition in contact with a polymer matrix, a filler of at least 1 micron particle size, and a blend of conductive nanoparticles. And placing the heat sink in contact with the thermally conductive composition. When the electronic component is a chip, the heat generating component is placed in contact with the printed wiring board and an electrical connection is formed between the component and one or more electrical contacts of the printed wiring board. A thermally conductive composition, which comprises a polymer matrix, a blend of at least 1 micron sized filler and conductive nanoparticles, is placed between the component and the printed wiring board so that the thermally conductive composition has one or more electrical connections. Seal. In another embodiment, the thermally conductive composition used to seal one or more electrical connections includes a blend of a polymer matrix and conductive nanoparticles.

  In other embodiments, a method for increasing heat transfer includes attaching a thermally conductive composition of the present disclosure to a semiconductor wafer having a plurality of die sites including a plurality of electrical contacts and a plurality of one or more solder balls. Disposing at the contact point. The thermally conductive composition is partially cured so that the apexes of one or more solder balls are exposed, and after that time, the wafer is cut into individual semiconductor chips. The individual chips are then placed on a printed wiring board so that one or more solder balls are aligned to form one or more electrical contacts and one or more electrical contacts on the printed wiring board. The components and wiring board are then heated to melt the solder balls and at the same time cure the thermal conductive composition, then cool them to solidify the solder balls, and the thermal conductive composition seals one or more electrical connections. The heat conductive composition is cured as follows.

  While the present disclosure has been illustrated and described with exemplary embodiments, it is not intended to be limited to the details shown because various modifications and substitutions can be made without departing from the spirit of the present disclosure. As such, further modifications and equivalents of the present disclosure disclosed herein may be made using routine experimentation for those of ordinary skill in the art, all such modifications and equivalents being defined by the following claims. It is believed that it is within the spirit and intent of this disclosure as specified.

1 is a cross-sectional view of a non-conductive TIM that includes both micron-sized filler particles and conductive nanoparticles. FIG. FIG. 2 is an enlarged view of a portion of FIG. 1 showing how conductive nanoparticles improve thermal conductivity between micron-sized filler particles and an electronic device. FIG. 4 is an enlarged view of a TIM cross section showing conductive nanoparticles that improve thermal conductivity between micron-sized filler particles. FIG. 4 is an enlarged view of a cross section of an electrically insulating underfill material that utilizes conductive nanoparticles that improve the thermal conductivity between micron-sized filler particles.

Claims (10)

A thermally conductive composition comprising a blend of a polymer matrix (16), one or more micron-sized fillers (18) and conductive nanoparticles (20), wherein the thermally conductive composition is non-conductive. (10). Micron sized fillers (18) from fumed silica, fused silica, finely divided quartz powder, amorphous silica, carbon black, graphite, diamond, hydrated alumina, metal nitride, metal oxide and combinations thereof The heat-conducting composition (10) according to claim 1, selected from the group consisting of: The thermally conductive composition (10) of claim 1, wherein the conductive nanoparticles (20) are selected from the group consisting of copper, silver, platinum, palladium, gold, graphite, aluminum, doped silicon and silicon carbide. Contacting the exothermic component (12) with a non-conductive thermal conductive composition (10) comprising a blend of a polymer matrix (16), one or more micron-sized fillers (18) and conductive nanoparticles (20) And place
A method of improving heat transfer comprising placing a heat sink (14) in contact with a thermally conductive composition (10). A heat generating component (12);
A heat sink (14);
Non-conductive comprising a blend of a polymer matrix (16), one or more micron-sized fillers (18) and conductive nanoparticles (20) inserted between the heat generating component (12) and the heat sink (14) An electronic component provided with a heat conductive composition (10). Place the heat generating component (30) in contact with the printed wiring board (34),
Contacting the component (30) with one or more electrical contacts of the printed wiring board (34) to form an electrical connection;
A thermally conductive composition (10) comprising a blend of a polymer matrix (16), one or more micron-sized fillers (18) and conductive nanoparticles (20) is formed into a component (30) and a printed wiring board (34). The method of improving the heat transfer property comprising disposing between, wherein the thermally conductive composition (10) seals one or more electrical connections. A thermally conductive composition (10) comprising a blend of a polymer matrix (16), one or more micron-sized fillers (18) and conductive nanoparticles (20), and a plurality of die sites having a plurality of electrical contacts. Coating on semiconductor wafers, including
One or more solder balls (32) are arranged at a plurality of contacts,
Partially curing the thermally conductive composition (10) so that the apex of one or more solder balls (32) is exposed;
Cutting the wafer into individual semiconductor chips,
One or more semiconductor chips are placed on the printed wiring board (34) such that the one or more solder balls (32) are aligned with the one or more electrical contacts of the printed wiring board (34) to form one or more electrical connections. Arranged,
Heating one or more semiconductor chips and the wiring board (34) so that melting of the solder balls (32) and curing of the heat conductive composition (10) occur simultaneously;
One or more semiconductor chips and wiring boards (34) so as to solidify the solder balls (32) and cure the heat conductive composition (10) so that the heat conductive composition (10) seals one or more electrical connections. Cooling),
A method of improving heat transfer properties comprising: Applying a heat conductive composition (10) comprising a blend of polymer matrix (16) and conductive nanoparticles (20) to a printed wiring board (34);
The one or more solder balls (32) and the one or more electrical contacts such that the one or more solder balls (32) are aligned with the one or more electrical contacts of the printed wiring board (34) to form one or more electrical connections. A heat generating component (30) including
The component (30) and the wiring board (34) are heated so that the melting of the solder sphere (32) and the curing of the heat conductive composition (10) occur simultaneously,
The component (30) and the wiring board (34) so that the solder ball (32) is solidified and the heat conductive composition (10) is cured so that the heat conductive composition (10) seals one or more electrical connections. To cool,
A method of improving heat transfer properties comprising: A heat generating component (30);
A printed wiring board (34);
An electronic component comprising a heat conductive composition (10) inserted between a heat generating component (30) and a printed wiring board (34) and comprising a blend of a polymer matrix (16) and conductive nanoparticles (20). A non-conductive underfill composition comprising a blend of a polymer matrix and conductive nanoparticles (20).

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